Apparatus for recording and reproducing sound



Aug. 21, 1928. 1,681,721

C. BLIEBERGER APPARATUS FOR RECORDING AND REPRCDUCING SOUND Filed March28, 192: z Sheets-Sheet 1 H l lllllllfl .Aug. 21, 1928.

' c. BLIEBERGER APPARATUS FOR nmconnme ANDREPRODUCING sounn 2Sheets-Sheet 2 to it, a recording stylus.

Patented Aug. 21, 192&

UNITED STATES PATENT OFFICE.

CHARLES BLIEBEBGER, OF ,NEW YORK, N. Y., ASSIGNOR OF FORTY-FI'VE PERCENT '10 ADOLPH R. THOMAS, OF NEW YORK, N. Y.

APPARATUS FOR' RECORDING AND REPRODUCING SOUND.

Application filed March 28,}923. Serial No. 628,196.

The object of my invention is to produce an apparatus capable ofrecording and reproducing sound in a better and more efficient way thanhas been possible with recording and reproducing devices heretoforeconstructed.

The precise details in the methods and mechanisms employed byphonograph'companies for the recording of sound are usually matters ofsecrecy, but it is generally known that the recording machinesheretofore in use embody a small disk or diaphragm which carries, or hasoperatively connected The diaphragm, usually of glass, is arranged atthe small end of a horn or'funnel, so as to receive the concentratedenergy of the sound waves that enter the larger end of the horn. In therecording process, the stylus cuts a spiral track in the surface of ablank disk composed of suitable material. The track made by the styluscorresponds to the vibrations .of the diaphragm.

The recording of sound as thus carried out has always presented seriousdifficulties and objections in the use of the small glass diaphragm,which is the most important element of the recording mechanism. Thesediaphragms generally range in size from about 1% to 2 inches indiameter, depending upon the particular kind of sounds to be recorded.If any sound wave strikes the diaphragm with a force or impact greaterthan the capacity of the diaphragm to respond to it, the result isover-vibration of the diaphragm with a corresponding defect in therecord. This defective action-of the diaphragm is commonly calledblasting or shattering, and has been referred to as the bugbear ofrecording. 1

- Also, a diaphragm sensitive to high notes would not be equallysensitive to low notes, and vice versa, so that the recording ofinstrumental or vocal selections encompassing the base and trebleregisters would be corrcspondingly faulty. I

Furthermore, even aside from the foregoing objections, the recordingdiaphragms heretofore employed require a concentration of sound wavesupon a very small, area. Now. this concentration or compressioninevitably distorts the sound waves and produces a record in which thedelicate overtones of the original sounds are lost or distorted. Sothat, when the record is played,-

the reproduction is not faithful to the original.

What I defects in the operation of prior recording diaphragms applieslargely to reproducing diaphragms used in phonographs, loudspeakingtelephone receivers, radio loudspeakers, and other similar acousticdevices. The diaphragms heretofore employed in sound-reproducingapparatus were properly sensitive only within restricted limits ofvibration. For instance, diaphragms that gave good results for hightones did not respond faithfully to low tones. Also, diaphragms good forvocal music would not give the best results in reproducing instrumentalselections. V

The foregoing and other defects and objections inherent in priorrecording and reproducing machines are effectively overcome b myinvention, which is characterize by a diaphragm of greater acousticcapacity and sensitiveness than diaphragmsheretofore employed. My newdiaphragm is capable of vibrating in consonance with sound waves of highintensity without blasting or shattering. The construction of thisdiaphragm is such that it is equally sensitive, within practical limits,to vibrations of low and high frequency.

Briefly stated, the diaphragm of my acoustic device comprises a stiffsection at the center and. a plurality of thin flexible sections nearthe periphery. The stiff and thin sections are of substantial areas andconstitute in effect two diaphragms-astitf diaphragm most sensitive toone band of frequencies, and a thin flexible diaphragm that respondsmost effectively to another band of frequencies. As a result, I producea diaphragm that is equally sensitive (within practical limits) to hightones and low tones. One way of forming this diaphragm is to provide thesame on its surface with depressions or cut-out sections to formsubstantial areas of less thickness than the other ortions of thediaphragm. These thinne and stiff sections render the diaphragm highlysensitive to vibrations within a wide range, whether the diaphragm isused for recording or reproducing. Where have said about thedifiiculties and I the diaphragm is not provided with these thinsections, it is of relatively greater thickness andcorrespondingstiffness. The main stifl section is at the center, and the thinflexible sections surround the stiff central section. There are variousways of 'constructing this double-acting diaphragm. In my experiments Ihave found that the best results are produced with a disk having thinnedareas or depressions on both sides and arranged in staggered relation.Also, I prefer to have some of the thinned areas extend nearer thecenter of the disk than others, although that is not essential. Thereare various ways of arranging these thin sections for the best results,depending in a large measure on the size and material of the diaphragm.As will appear later, the diaphragm may be constructed of a suitablemetal or non-metallic material. I have obtained highly satisfa"toryresults with diaphragms of maple wood.

When my new diaphragm is used for recording I prefer to construct it ofcomparatively large working area, so as to obviate the objectionablecondensation of sound waves necessary in prior recording devices. As aresult, I obtain a true and faithful record In employing my inventionfor reproducing sound, I may use a large diaphragm, as in recording, orI may use a diaphragm to fit an ordinary sound-box or telephoneloudspeaker. A large diaphragm for phonographs requires no tone arm andno horn.

My invention also comprises new and novel connections between the largeform of diaphragm and the recording or reproducing stylus, whereby thelatter operates in strict conformity with the vibrations of thediaphragmfor recording, and vice versa in reproducing. These connectionsare such as to adapt my apparatus for playing lateral cut records andhill and dale records equally well without any adjustment or separateattachment.

The above and other advantages and novel characteristics of my inventionwill be clearly understood from a detailed description of theaccompanying drawings, which illustrate several embodiments of myinvention.

In these drawings,

Figure 1 shows a sectional View, approximately on line 11 of Fig. 2, ofa phonograph cabinet provided with a large reproducing diaphragmembodying my invention;

Fig. 2 is a viewat right angles to Fig. '1, approximately on line 22 ofFig. 1, showing the diaphragm in face view;

Fig. 3 is an enlarged view of the diaphragm in cross-sectiontakenapproximately on line 33 of Fig. 2, the thickness of the diaphragmbeing exaggerated to show the depressions or thinned portions moreclearly;

Fig. 4 is a side view of a small diaphragm constructed in accordancewith my invention and mounted in a sound'box;

Fig. 5 is a cross-section on line 5-5 of Fig. 4:, but showin thediaphragm in exaggerated thickness for clearness;

Fig. 6 shows an enlarged cross-section approximately on line 6-6 of Fig.4:;

Figs. 7 8 and 9 illustrate three modifications of my new diaphragm;

Fig. 10 is an enlarged view in cross-section on line 1010 of Fig. 7;

Fig. 11 is an enlarged view in cross-section on line 1111 of Fig. 8; and

Fig. 12 is an enlarged view in cross-sea tion on line 1212 of Fig. 9.

I will first describe the construction illustrated in Figs. 1, 2 and 3.In a suitable framework F is rigidly mounted a disk or diaphragm D. Theframework F is here shown as consisting of a pair of boards or plates 1and 2, held together by bolts 3, or otherwise. 'The boards 1 and 2 areprovided each with a circular opening 4 and with an annular recess 5 toreceive the outer edge of the diaphragm. In this way, the diaphragm D isfirmly clamped between the boards 1 and 2 for vibratory movement. Iwould have it understood that the framework F repre-. sents any suitablemounting for the dia-- phragm. Personally, I prefer to have theframework of non-metallic material, as

wood, for instance. If the framework is of metal, it is better to inserta suitable nonmetallic packing between the metal and the clamped ed e ofthe diaphragm.

As seen from Figs. 2 and 3, the disk or diaphragm D is provided onitsworking surface with thinned sections or depressions marked a, b, c andd. Depressions a and b are formed on one side or face of the diaphragm,and depressions a and d on the other side. In the present instance thereare four depressions in each set or series, arranged in two concentricrings and in staggered or oif-set relation. Thus, the outer depressionsa are off-set with respect to the inner depressions 6. Similarly, theouter depressions 0 on the other side of the disk are off-set inrelation to the inner depressions Z. Also, the depressions a and-0 onopposite sides of the disk are in staggered relation,and the same istrue of the inner depressions b and (Z.

The diaphragm D is equally adapted for recording and reproducing. Forrecording, it is provided with a properrecording stylus, as will beunderstood by those familiar with that particular art. For reproducingpurposes, t e diaphragm has an attachement adapted to receive areproducing needle, as

in a phonograph. In Figs. 1, 2 and 3, I"

the diaphragm D at or near the center therea met by any suitable means.

of. The free end of rod 6 is provided with a lateral fork or extension6' on which is pivoted a rotatable sleeve or bushing 8 carrying a bentrod 9. To the free end of rod 9 is pivoted one end of a rigid bar or arm10. The lower end of this arm carries a suitable holder 11 adapted tosupport a needle or stylus 12 in correct position. In Figs. 1 and 2, theneedle 12 is shown in playing position on a record 13 supported on aturntable 14, which is driven by a motor M. All the parts are enclosedin a cabinet C of appropriate construction and design. The framework F,which carries the diaphragm D, is held in rigid position within the cab-I .have not deemed it necessary to illustrate or describe such holdingmeans, as that is obvious to any phonograph builder.

It will be clear that the parts 6, 8', 9, 10 and 11 constitute a rigidconnection between the needle 12 and the vibratory diaphragm D, wherebythe movements of the needle as it travels over the record arecommunicated to the diaphragm. The horizontally swinging sleeve 8 andthe vertically swing arm 10 constitutes a universal joint in theconnection between the needle and the diaphra m, so that the lateral aswell as the vertical movements of the arm 10 are communicated to thediaphragm. This makes it possible to play lateral cut,r'ecords and hilland dale records equally well and without any change or adjustment inthe connections, as Ihave actually demonstrated. Of course, the properneedle .or stylus must-beused with eachmake of record. I would have itunderstood that the arrangement and construction of parts 6, 8, 9 and 10are to be regarded merely as illustrative and not in a restrictivesense.

The depressions a, b, c and c5 of diaphragm D form sections of lessthickness than the other portions of the diaphragm, and these thin areasincrease the acoustic sensivity and capacity of the diaphragm. I haveshown this by actual tests. The high notes of a violin are reproduced asclearly and faithfully as the deep tones of a bass instrument, and vocalmusic is reproduced with the same natural quality as instrumental.

The above advantages and characteristics render my diaphragmparticularly .applicable in recording, where it receives the sound wavesto be recorded and transmits them to a recording stylus. Prior recordingmachines have always presented certain difficulties and objections, thechief among which are the unnatural concentration of the sound waves tobe recorded, the inability of the small glass diaphragm to respond tohigh and low tones with the same degree of efiiciency, and blasting ofthe diaphragm under robust tones. The small glass recording diaphragmsheretofore used have required a jamming (so to speak) of the sound wavesthrough a narrow tube against the diaphragm. Obviously, the vibrationsof a diaphragm under such conditions could not faithfully reproduce theoriginal tones. Also, the rigidity of those small diaphragms has made itimpossible, as far as I know, to record faithfully the soft delicatetones of certain instruments. For instance, it is .a fact that the tonesof aviolin are too weak to actuate the old recording diaphragms withsuflicie'nt energy. For this reason it has been found necessary to use aspecially constructed recording violin, one type of which is known asthe Stroh violin. This instrument is provided with a diaphragm and anamplifying horn to intensify the tones. Such a freak instrument doesnot, of course, give out true violin music.

The foregoing and other objections and difficulties of prior recordingmachines and methods are overcome by the use of my d1aphragm. In thefirst place, this diaphragm presents a considerable surface area to thesound wave to be recorded, and does not, therefore, require an unnaturaland objectionable concentration of sound waves, as heretofore necessarywith small diaphragms, Of course, a sound-directing tube or funnel forguiding the waves against the diaphragm without unduly concentratingthem, may be used to prevent unnecessary dissipation of sound Waves.

In the double-acting diaphragm of my invention, the outer area--that is,the area or surface nearer the periphery is rendered highly sensitive tosound waves by means of thinned or scooped out sections, as exemplitiedby the depressions a, b, c and d previously described. These thinnedsections impart a flexibility to the diaphragm as a whole, withoutweakening it mechanically, thereby giving it a greater degree ofresponsiveness to acoustic impulsesthan that of prior diaphragms.Consequently, my diaphragm responds correctly to the softest tonesrequired to be recorded-such as those of a regular violin, a pianoforte,and other stringed instruments, which have heretofore presenteddifiiculties in recording.

The acoustic capacity of my diaphragm is such-that it does not blast orshatter under intense sound waves, like those produced by a strong voiceor a brass instrument. The precautions and subterfuges hereintoforerequired to prevent blasting of the small diaphragms in recording robusttones are not necessary in the use of my invention. This enables me tosecure a correct and true record of the original sounds over as wide arange as occurs in practice.

The diaphragm D may be of any suitable material, metallic ornon-metallic. Personally, I prefer a diaphragm of wood, renderedmoisture-proof by any suitable means. In

my experiments and demonstrations, I obtained very satisfactory resultswith diaphragms of maple having a working diameter of about 11% inchesand a thickness of about 7 to of an inch. The precise thickness of anydiaphragm depends upon the material used, upon the working diameter ofthe diaphragm, and also upon the particular acoustic effect desired.

With a diaphragm like that shown in Figs. 1, 2 and 3, which illustrate areproducing apparatus that I have used in actual practice, no horn orother amplifying device is necessary, for the vibrations of thediaphragm are sufficiently strong to produce sounds o ample volume.

In Figs. ei12, I have shown several. embodiments of small diaphragms foruse in phonograph sound boxes, radio receiving telephones, and the like.

In Figs. 4, 5 and 6, the diaphragm I) is mounted in a. casing 15, whichin this instance is in the form of a phonograph sound box. Diaphragm Dhas spaced depressions or thinned sections 16 on one side and similardepressions 17 on the other side. These depressions radiate from nearthe center toward the periphery and are in staggered. arrangement.

In Figs. 7 and 10, there is a diaphragm D having spaced depressions 18on one side and like depressions 19 on the other side.

In Figs. 8 and 11, the diaphragm D is provided with a pair ofdepressions or thinned sections 20 on one side and similar sections 21on the other side.

In Figs. 9 and 12, there is a diaphragm I) provided with a series ofdepressions or thinned sections22 and an intermediate series of thinnedsection 23. The depressions 22 extend nearer to the center of thediaphragm than the depressions 23. As may be seen from Fig. 9, the areaof the thick central section of diaphragm D is about equal to thecombined area of the thin sections 22 and 23, and these thin sectionsare about half as thick. as the central section.

What I have said about the operation and advantages of diaphragm Dapplies to the smaller diaphragms D, D D and D which are merelyillustrative of some of the forms in which my invention may be embodied.

A phonograph or telephone loud-speaker equipped with the diaphragm of myinvention gives a reproduction of superior quality, characterized by afidelity and clearness of tone. The distortion and metallic harshness,inherent in tones reproduced by the old mica dia-phragms, which are usedin nearly all phonographs and telephone loudspeakers, are absent in areproducer containing my new diaphragm. ,In my opinion, the mostpleasing tones are given by a diaphragm of wood, especially one ofmaple,

but an ordinary wooden disk does not give by a diaphragm of metal.

I magnetic poles.

satisfactory results. To make such a disk sensitive, it must be madequite thin and,

therefore, very frail. This renders the disk liable to break easily and.furthermore, does not produce sounds of suflicient volume. Thereproduction is too thin as we say; it lacks body and power. On theother hand, by increasing the thickness of such a disk, you increase itsrigidity and correspondingly decrease its ability to respond properly.to vibratory impulses.

The disk or diaphragm of my invention overcomes these difficulties. forreasons already explained, and so I am enabled to employ a diaphragm ofwood or other suitable non-metallic material. I Vhile I have madespecial reference to a diaphragm constructed of wood, I have done somerely to point out one of the advantages of my invention. and not byway of limitation. To a musically trained ear the quality ofreproduction givenby a diaphragm of wood, such as maple, is usuallypreferable to that given The same is true as to recording. However, inthe broad aspect of my invention, the diaphragm may be made of anymaterial capable of being provided with thinned sections or depressionson its surface and capable of vibratory action in recording orreproducing sound.

It will be noticed that in all the examples of my new diaphragm as abovedescribed, there is a central stiff section of substantial area at thecenter and a plurality of thin flexible sections around the centralsection, these thin sections being separated by ribs or webs radiatingfrom the central section. The thin flexible sections constitute adiaphragm of low natural frequency, and the thick stiff sections form adiaphragm of high natural frequency to encompass the entire range ofmusical tones used in practice. I use the terms stiff and flexible in arelative sense. That is to say, the thick section is stiff as comparedwith the thin sections, and the thin sections are more flexible than thethick section. I

In Figs. 4 and 5, the needle-actuated arm or lever 24 is representativeof any means for. vibrating the diaphragm. In electromagnetic soundreproducers, as in the telephone and radio arts, the diaphragm, if madeof non-magnetic material, is suitably connected with the vibratingarmature of an electromagnet. If the diaphragm is constructed ofmagnetic material, it is usually arranged to be directly influenced bythe These things are well understood by the skilled electrician.

It is obvious that the basic principle of my invention may becarried'out in other ways than herein set forth by Way of example. Thesize, form and arrangement of the depressions or thin sections of thediaphragm may be varied and will in each case depend upon the size andmaterial of thediaphragm, the particular purpose for which I thediaphragm is used, the acoustic effect desired, and perhaps otherfactors that may come up in a given instance.

' I claim as my invention:

1. A homogeneous diaphragm consisting of a stiff section at the centerand a plurality of radially spaced thin flexible sec-- tions near theperiphery, said stiff and said thin sections being of substantial areasso as to constitute vibratory surfaces, the stiff section being mostsensltive to one band of frequencies and the thin sections mostsensitive to another band of frequencies.

2. A' homo 'eneous acoustic diaphragm composed of flat sections of twodifferent thicknesses and of correspondingly different degrees offlexibility, the thick sections and the, thin sections being'so arrangedand of such area as to constitute respectively a stiff diaphragm of highnatural frequency and a flexible diaphragm of low natural frequency.-

3. A homogeneous acoustic diaphragm having a thick central sectionsurrounded by a thin fiat section of about the same area as said thicksection, said thick and thin secacting like a flexible diaphragm mostsen-' sitive to low notes. v

5. A homogeneous acoustic diaphragm comprising a circular centralsection of thickness and substantial area, and a plurality of segmentalsections surrounding said central section and considerabl thinner thanthe central section, said thic central section and said thin segmentalsections acting respectively like a stiff diaphragm of high naturalfrequency and like a flexible diaphragm of low natural frequency.

6. A homogeneous acoustic diaphragm having a thick fiat section at thecenter and a plurality of thin flat sections surrounding said thicksection, the area of said thick section bein about equal to the combinedarea of the thlnsections, the thick section being about twice as thickasthe thin sections, and each of said'thick and thinsections being ofapproximately uniform cross-section, whereb I said thick section actslike a stiff 'diae pliragm most sensitive to one band of frequencies andsaid thin sections act like a flexible diaphragm most sensitive to adifferent band of frequencies.

7. An acousti diaphragm having a thick' central section of substantialarea, radially extending portions radiating from said central. sectiontoward the periphery and 'Of substantially the same thickness as saidcentral section, and thin sections of substantial area formed betweensaid radially extending portions alternately on opposite sides of thediaphragm, said thin sections acting like a flexible diaphragm mostsensitive to low.

tones and saidrthick section acting like a stiff diaphragm mostsensitive to high notes. 8. A disk shaped acoustic diaphragm composed oftwo portions having diflerent degrees of flexibility whereby the morestiff portion responds to relatively high frequencies and the moreflexible portion responds 7 to relatively low frequencies, themore'stifi? portion comprising a' rim at the periphery of the disk, asubstantially circular center portion spaced from-said rim, andcircumferentially spaced radially extending portions connecting said rimwith said center portion; and the more flexible portion compositionedbetween the radially extending stiifportions and between the relativelystiff rim and center portions.

9. A disk shaped acoustic diaphragm composed of two portions ,havingdifferent degrees of flexibility whereby the more stiff portion respondsto relatively high frequen-. cies and the more flexible portion respondsto relatively low frequencies; the more stiff portion constituting abouthalf of the area of the diaphragm and comprising the center portion ofthe diaphragm; and the more" flexible portion comprisingcircumferentially extending zones positioned between the relativelystiff center portion and the edge of the diaphra m;

C I LES'BLIEBERGER] prising circumferentially extending zones;

